Re: Simple Vector file format for Web?

lilley (
Mon, 31 Jul 95 12:56:08 EDT

Martin J Duerst points out:

> These formats are in no way "Simple Vector file formats" as the subject
> suggests! Most CAD packages can output subsets of some of these
> standards, and can then read back what they wrote. But you are very
> lucky if a package can read what another package wrote, even
> if both use the same standard.

Unless both use the same application profile, which is designed
specifically to allow this sort of interchange by specifying
a subset functionality for writers, and an increased capability
for conforming readers.

A CGM which claims to have been written in accordance with a
particular application profile can be validated against that profile.
If a reader which claims conformance cannot read such a valid CGM, the
fault is with the reader. If the CGM failed the conformance test, the
fault is with the writer.

The registration request for CGM stated that a profile would be used:

It is proposed that the Model Profile, as specified in IS 8632:1992
Amendment 1( 1994), be the profile. It is proposed that the CGMs
use the binary encoding, as specified in IS 8632:1992 Part 3.

> However, it is clear that the main problem when trying to support
> a full standard is the complexity of these standards. If most CAD
> systems don't give full support for reading, I doubt whether an
> average or even a high-end WWW browser will ever be able to
> offer this functionality.

With a monolithic browser this may well be true. There have been
a number of proposals for devolved functionality among cooperating

Furthermore, there is no reason why other profiles should not be used
with a suitable parameter, or why CAD packages should not be used as
external viewers in such a case, if more extended functionality is

Chris Lilley, Technical Author
|       Manchester and North HPC Training & Education Centre        |
| Computer Graphics Unit,             Email: |
| Manchester Computing Centre,        Voice: +44 161 275 6045       |
| Oxford Road, Manchester, UK.          Fax: +44 161 275 6040       |
| M13 9PL                            BioMOO: ChrisL                 |
|     URI:       |